Mercury, the smallest planet in the solar system, is continuing to shrink at a rate faster than previously estimated, according to a new study. With a radius of approximately 1,516 miles, Mercury is about one-third the size of Earth and roughly 1/29th the width of Jupiter. Scientists now suggest that the planet may have contracted by as much as 14.5 miles since its formation around 4.5 billion years ago.
The recent findings were published in Geophysical Research Letters and provide new insights into the thermal and geological evolution of Mercury and similar planetary bodies. Researchers led by planetary scientist Gaku Nishiyama of the German Aerospace Center Institute of Space Research analyzed high-resolution images and digital elevation models derived from NASA’s Messenger spacecraft, which conducted a flyby of Mercury in 2004.
Mercury’s shrinkage results from the gradual cooling and contraction of its large metallic core, which causes the planet’s surface to deform, forming characteristic ridges and valleys often described as planetary “wrinkles.” While previous studies estimated Mercury’s contraction at a few miles, the latest research finds that the planet may be shrinking up to 30 percent faster than earlier calculations indicated.
Dr. Nishiyama noted that this level of shrinkage is significant compared to other bodies in the solar system such as the Moon and Mars, which are also experiencing surface contractions but at comparatively lower rates due to their different internal compositions. The large iron core of Mercury plays a key role in its ongoing reduction in size.
The study also highlighted challenges in accurately measuring Mercury’s shrinkage because surface features like lava deposits and impact debris can obscure the wrinkles formed by planetary contraction. Researchers depend primarily on observable topography, which limits the precision of current estimates.
Further data and enhanced imaging of Mercury’s surface will be necessary to refine these measurements and improve understanding of how rocky planets cool and contract over billions of years. Scientists emphasize that the updated shrinkage estimates contribute to broader knowledge of planetary formation and evolution processes within the solar system.